22, 
and are both attached to anterior projections from the 
prefrontals in the manner described above. 
The suborbital and supratemporal chains of lateral 
line ossicles are described with their respective sensory 
canals. 
2.—TuHE Patato-Prerycorp ArcaDE (Fig. 5). 
Ocular Side. 
Hyomandibular ({7m.)—This bone articulates with 
the skull in two ways. First by a well marked ball and 
socket joint situated at the anterior extremity of its 
articular surface, and second by a !ong and less con- 
spicuous facet behind this. The socket is a deep depres- 
sion very obvious in dried skulls and situated between the 
sphenotic and prootic. From this depression the other 
facet passes upwards and backwards, and is placed mostly 
if not entirely on the pterotic. The head of the hyoman- 
dibular is cartilaginous in three places, at the two facets 
for the skull and at the projection articulating with the 
operculum. Parallel with the posterior edge, and at a 
short distance from it, is a stout bony ridge (the most 
strongly calcified part of the bone) which is closely 
attached to the pre-operculum. In front of this a shaft — 
of cartilage passes downwards and forwards, which bears 
a thin cartilaginous cap, and articulates with the inter- 
hyal in such a way as to admirably illustrate what is now 
a commonplace of vertebrate morphology, that the 
hyomandibular is the modified dorsal segment of the hyoid 
arch, which has in many forms lost its connection with 
the hyoid arch, and has acquired on the one hand a con- 
nection with the auditory capsule and on the other with 
the jaw suspensorial apparatus. The Plaice is therefore 
hyostylic. The remainder of the ventral edge of the 
